Method for Coating Components

ABSTRACT

A method for coating components, particularly engine components, includes the steps of: producing a coating material by or when melting, fusing and/or incipient melting a material, for a first coating method; and using this coating material at least partly in a second coating method.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of PCT International Application No. PCT/EP2018/075937, filed Sep. 25, 2018, which claims priority under 35 U.S.C. § 119 from German Patent Application No. 10 2017 220 522.9, filed Nov. 17, 2017, the entire disclosures of which are herein expressly incorporated by reference.

BACKGROUND AND SUMMARY OF THE INVENTION

The present invention relates to a method for coating components, to a use of a coating process and to a coating material.

The components/assemblies at issue are in particular cylinder heads of internal combustion engines. In order to prevent valves becoming embedded in the cylinder head for example, so-called valve seat rings manufactured from a sintered material for example are often provided. It is also known to form the valve seats for the valves directly on the cylinder head using suitable coating processes, cf. for example DE 199 60 884 A1. Processes known in this connection include inter alia thermal spraying processes, such as high velocity oxygen fuel spraying (HVOF) or laser deposition welding. A feature common to the known processes is that they unfortunately have high resource input requirements.

The present invention accordingly has for its object to provide a process for coating components, a use of a coating process and a coating material which in particular feature low resource input requirements.

This object is achieved by a method, by a use and by a coating material in accordance with the claimed invention.

According to the invention a method for coating components, in particular engine components, comprises the steps of: producing a coating material by or during melting or incipient melting of a feedstock for a first coating process; and at least partially using the coating material for a second coating process.

Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a highly schematic flow diagram illustrating the method according to an exemplary embodiment of the invention.

DETAILED DESCRIPTION OF THE DRAWING

Referring to FIG. 1, a method for coating components, in particular engine components, includes the steps of: producing a coating material by or during melting or incipient melting of a feedstock for a first coating process (S1); and at least partially using the coating material for a second coating process (S2).

This makes it possible to realize a very cost-effective and resource-efficient coating process. The second coating process is advantageously a process distinct from the first coating process. This has the particular advantage that the coating material is formed effectively as a byproduct of the first coating process and is/may be further used for the second coating process.

The method preferably further comprises the step of: melting or incipiently melting a wire feedstock for a coating process. A wire feedstock is to be understood as meaning any electrically conductive feedstock in wire form. Alternatively, feedstocks in powder, wire, cable and/or rod form may also be melted or incipiently melted in the process. Energy sources used for the melting or incipient melting are for example an electrical arc, a plasma jet, an oxygen-fuel flame, a high velocity oxygen-fuel flame, high velocity preheated gases or a laser beam.

In a preferred embodiment, the second coating process is cold gas spraying. Cold gas spraying is a coating process in which the coating feedstock is applied to a carrier material in powder form at a very high velocity. In one embodiment a process gas heated to a few hundred degrees Celsius (nitrogen or helium) is accelerated to supersonic velocity by expansion in a laval nozzle and the coating material is then injected into a gas jet. This accelerates the injected coating material to such a high velocity that upon impacting the substrate it forms a dense and firmly adherent layer. The cold processing ensures inter alia that the constituents of the coating material do not melt. Preferred process pressures here are about 20 to 80 bar, preferably about 45 bar. Velocities of about 750 to 1700 m/s, preferably of about 1000 to 1250 m/s, are achieved upon ejection from the coating gun.

It has surprisingly been found that especially during melting of wire feedstock a powder/coating material which is very suitable for cold gas spraying in particular is formed or may be generated.

In a preferred embodiment, the first coating process is a thermal spraying process, in particular wire arc spraying. This comprises producing an arc between two spraying feedstock wires of the same or different types. The wire tips are melted at a temperature of about 4000° C. and blown onto the prepared workpiece surface using atomizer gas. Using nitrogen or argon instead of air as the atomizer gas reduces oxidation of the materials. The second coating process is preferably used for forming or coating valve seats of internal combustion engine cylinder heads. The process is thus particularly advantageous since the wire arc spraying process, i.e. the first coating process, is preferably used as a process for coating cylinder bore surfaces. This makes it possible to realize a particularly lean and resource-efficient production process.

In one embodiment, the method comprises the steps of:

-   -   producing the coating material during performance of the first         coating process;     -   collecting the coating material during or after performance of         the first coating process.

In other words, in one embodiment a first coating with wire arc spraying is performed which indirectly, through the thus performed melting of a wire feedstock, forms/produces the coating material. It has been found that melting of wire feedstock, as is performed in thermal spraying processes such as wire arc spraying, forms an ideally structured coating material especially for cold gas spraying.

In one embodiment, the method comprises the step of:

-   -   performing the first coating process in an inert atmosphere, in         an oxygen-free environment or in an at least oxygen-poor         environment.

This advantageously allows oxidation of the coating material to be avoided or at least minimized.

In one embodiment, the method comprises the step of:

-   -   processing the coating material for the second coating process.

The processing comprises for example cleaning, filtering, sieving, separating and/or mixing the coating material. It is advantageously possible to employ purely mechanical processing measures while avoiding the need to use chemicals or the like.

In one embodiment, the method comprises, especially having regard to the abovementioned processing, the steps of:

-   -   sieving to a defined size;     -   packaging in an inert atmosphere/in an oxygen-free or         oxygen-poor environment.

In one embodiment, the method comprises the steps of:

-   -   performing the first coating process in an extracted enclosure;     -   extracting and storing the, especially excess, coating material.

The above method steps show that the method advantageously requires no elaborate equipment, apparatuses or the like.

In one embodiment, the method comprises the steps of:

-   -   providing a cylinder head and a crankcase;     -   coating the crankcase, in particular the cylinder bores of the         crankcase, in the first coating process;     -   coating the cylinder head, in particular at least a valve seat         of the cylinder head, in the second coating process.

The method advantageously comprises the step of:

-   -   temporal and/or spatial separation of the first and second         coating process.

This advantageously allows greatest flexibility when using the method.

The invention also provides for the use of a first coating process for producing a coating material for a second coating process distinct therefrom.

The advantages mentioned in connection with the method apply analogously/correspondingly to the use.

In one embodiment, the method is carried out as follows:

applying a first and a second coating onto an assembly, wherein the first coating is produced by a first coating process and wherein the second coating is produced with coating material from the first coating process. The first and second coating processes are distinct from one another. In a preferred embodiment, the assembly comprises a cylinder head and a crankcase, wherein the cylinder head comprises at least one valve seat which comprises the second coating and wherein the crankcase comprises at least one cylinder bore which comprises the first coating. The assembly is thus in particular an engine comprising the cylinder head and the crankcase, wherein the bores of the crankcase are coated by means of a thermal spraying process, in particular wire arc spraying, and wherein the thus produced excess coating material is used for coating the valve seats of the cylinder head.

In one embodiment, a thickness of the second coating is in a range of about 50-400 μm, in particular in a range of about 200-300 μm. Depending on the desired total thickness the coating may be applied in two or more layers each having a thickness of for example about 50 μm.

In one embodiment, at least one valve seat is an inlet valve seat and at least one valve seat is an outlet valve seat, wherein a thickness of the first coating and/or a composition are different at the inlet and the outlet. Depending on the process mode it is very easy to accommodate the different requirements of the coating through a different process regime. This different process regime may manifest for example in an adjustment of the composition of the coating material for the cold gas spraying or in a different configuration, for example in terms of the thickness of the coating.

In one embodiment, the method comprises the step of:

-   -   limiting a surface temperature during the second coating process         to about 150° C.

Since during the cold gas spraying there are no high thermal or mechanical stresses on the surface to be coated, in the present case especially on the valve seat of the cylinder head, said seat need not be especially adapted or reinforced either. This allows the cooling channels to be brought closer to the combustion chamber and to the valve(s), thus allowing improved cooling of the engine. The weight of the cylinder head can also be reduced since the mechanical and thermal stresses to which it is subjected are smaller.

The invention also provides a coating material produced by a method according to the invention, wherein the coating material is pulverulent, in particular spherical.

A powder/particle diameter is advantageously in a range from about 5 to 150 μm, particularly preferably in a range from about 20 to 50 μm.

In one embodiment, the coating material is an Fe-based powder having an Fe proportion of at least 94%. Further constituents are for example C, S1, Mn, Cr, Ni and Cu. A powder having an Fe proportion in a range from at least about 68%, wherein the Cu proportion is up to about 14%, is alternatively employed. Further constituents are for example C, Co, Mo, Ni, Cr, Mn and S.

The advantages mentioned in connection with the method and in connection with the use apply analogously and correspondingly to the coating material and vice versa as well as in combination.

The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof. 

What is claimed is:
 1. A method for coating components, comprising the steps of: producing a coating material by or during melting or incipient melting of a feedstock for a first coating process; and at least partially using the coating material for a second coating process.
 2. The method according to claim 1, further comprising the step of: melting or incipiently melting a wire feedstock.
 3. The method according to claim 2, wherein the second coating process is cold gas spraying.
 4. The method according to claim 1, wherein the second coating process is cold gas spraying.
 5. The method according claim 1, wherein the first coating process is a thermal spraying process.
 6. The method according claim 5, wherein the thermal spraying process is wire arc spraying.
 7. The method according to claim 1, further comprising the steps of: producing the coating material during performance of the first coating process; and collecting the coating material during or after performance of the first coating process.
 8. The method according claim 1, further comprising the step of: performing the first coating process in an oxygen-free environment or in an at least oxygen-poor environment.
 9. The method according to claim 1, further comprising the steps of: performing the first coating process in an extracted enclosure; and extracting and storing the excess coating material.
 10. The method according to claim 1, further comprising the steps of: providing a cylinder head and a crankcase; coating the crankcase in the first coating process; and coating the cylinder head in the second coating process.
 11. The method according to claim 1, further comprising the step of: separating the first and second coating processes spatially and/or temporally.
 12. The method according to claim 1, wherein the coating components are engine components.
 13. A method of use, comprising: use of a first coating process for producing a coating material; using the coating material for a second coating process.
 14. A coating material produced by a process according to claim 1, wherein the coating material is pulverulent.
 15. The coating material according to claim 14, wherein a majority of the particles have a diameter of 5 to 150 μm.
 16. The coating material according to claim 14, wherein a majority of the particles have a diameter of 15-80 μm.
 17. The coating material according to claim 14, wherein the coating material has an Fe proportion of at least 94%.
 18. The coating material according to claim 14, wherein the coating material has an Fe proportion of at least 68% and a Cu proportion of up to 14%. 